1. Field of the Invention
The present invention relates to cured, dual layered dielectric films and to a process for their production. More particularly, the invention pertains to dual layered dielectric films in which a lower layer comprises a non-silicon containing organic polymer and an upper layer comprises an organic, silicon containing polymer. Such films are useful in the manufacture of microelectronic devices such as integrated circuits (IC""s).
2. Description of the Related Art
A continuing trend in the field of semiconductor technology is the formation of integrated circuit chips having more and faster circuits thereon. Such ultralarge scale integration has resulted in a continued shrinkage of feature sizes with the result that a large number of devices are available on a single chip. With a limited chip surface area, the interconnect density typically expands above the chip substrate in a multi-level arrangement and so the devices have to be interconnected across these multiple levels.
The interconnects must be electrically insulated from each other except where designed to make contact. Usually electrical insulation requires depositing dielectric films onto a surface. It is known in the art that siloxane resins are useful in the electronic and semiconductor fields to provide a dielectric coating to silicon wafers and other components. Such coatings protect the surface of substrates and form dielectric layers between electric conductors on IC""s. Such coatings can be used as protective layers, interlevel dielectric layers, doped dielectric layers to produce transistor like devices, capacitor and capacitor like devices, multilayer devices, 3-D devices, silicon on insulator devices, coatings for superconductors, and the like.
As mentioned above, semiconductor devices often have multiple arrays of patterned interconnect levels that serve to electrically couple individual circuit elements thus forming an integrated circuit. In the past, these interconnect levels have been separated by such insulating dielectric films as a silicon oxide film formed using chemical vapor deposition or plasma enhanced techniques. However, as the size of circuit elements and the spaces between such elements decreases, the relatively high dielectric constant of such silicon oxide films has become a problem.
In order to provide a lower dielectric constant than that of silicon oxide, dielectric films formed from siloxane based resins are becoming widely used. However, while such siloxane films do provide lower dielectric constants than silicon oxide films it has been found that typically the dielectric constants of such films are limited to those of approximately 3.0 or greater. The dielectric constant of such insulating films is an important factor where IC""s with low power consumption, crosstalk, and signal delay are required. As IC dimensions continue to shrink, this factor increases in importance. As a result, siloxane based resin materials that can provide insulating films with dielectric constants below 3.0 are very desirable. Furthermore, it would be desirable to have a siloxane based resin which have a high resistance to cracking and low stress when formed in thicknesses of approximately 0.1 xcexcm to about 1.0 xcexcm or greater.
In addition, in the production of microelectronic devices, SiO2, SiN or SiON are conventionally used as hardmasks or etch stops for the integration of low k organic films. The problem with using these films is that they have relatively high k values (xe2x89xa74.0) compared with the organic films ( less than 3.0). This invention describes the use of low k, siloxane based polymer films in the integration of low k organic films. This allows the effective dielectric constant to be lower than if conventional films are used.
The different chemical structure of siloxane based polymers compared to non-silicon containing organic polymers require different etch chemistries. Etch chemistries used for low k non-silicon containing organic polymer films typically do not etch siloxane based polymers, SiO2, or SiN dielectrics. Integration of organic polymers into subtractive aluminum, damascene or dual damascene schemes typically requires that a SiO2, SiN or SiON layer be placed on the organic polymer to act as an etch stop or hardmask to pattern vies and trenches. These layers have high k values (xe2x89xa74.0) and reduce the effectiveness of using low k organic polymers between metal lines. Using a low k siloxane based organic polymer in a manner similar to conventional SiO2, SiON or SiN films as a hardmask or etchstop will reduce effective interline capacitances. According to the invention, a high or low organic content siloxane film is spun onto either baked or cured films of a non-silicon containing low k dielectric film. The high or low organic content siloxane film is used as an etch-stop or a hardmask, similar to standard SiO2, SiON or SiN in a variety of integration techniques including subtractive aluminum, and damascene and dual damascene processes.
The invention provides a dielectric coated substrate such as a microelectronic device which comprises:
(a) a first dielectric composition film on a substrate which comprises a non-silicon containing or substantially non-silicon containing organic polymer; and
(b) a second dielectric composition film on the first dielectric film, which second dielectric composition comprises a polymer having a structure selected from the group consisting of I and II:
[Hxe2x80x94SiO1.5]n[Rxe2x80x94SiO1.5]m, 
[H0.4-1.0SiO1.5-1.8]n[R0.4-1.0xe2x80x94SiO1.5-1.8]m, 
[H0-1.0xe2x80x94SiO1.5-2.0]n[Rxe2x80x94SiO1.5]m, 
[Hxe2x80x94SiO1.5]x[Rxe2x80x94SiO1.5]y[SiO2]z,xe2x80x83xe2x80x83I. 
wherein the sum of n and m, or the sum or x, y and z is from about 8 to about 5000, and m and y are selected such that carbon containing substituents are present in an amount of less than about 40 Mole percent; and wherein R, is selected from substituted and unsubstituted straight chain and branched alkyl groups, cycloalkyl groups, substituted and unsubstituted aryl groups, and mixtures thereof;
[HSiO1.5]n[RSiO1.5]m, 
[H0.4-1.0SiO1.5-1.8]n[R0.4-1.0SiO1.5-1.8]m, 
[H0-1.0SiO1.5-2.0]n[RSiO1.5]m,xe2x80x83xe2x80x83II. 
wherein the sum of n and m is from about 8 to about 5000 and m is selected such that the carbon containing substituent is present in an amount of from about 40 Mole percent or greater; and
[HSiO1.5]x[RSiO1.5]y[SiO2]z; 
wherein the sum of x, y and z is from about 8 to about 5000 and y is selected such that the carbon containing substituent is present in an amount of about 40 Mole % or greater; and wherein R, is selected from substituted and unsubstituted straight chain and branched alkyl groups, cycloalkyl groups, substituted and unsubstituted aryl groups, and mixtures thereof.
The invention also provides a process for forming a dielectric coating on a substrate, such as a microelectronic device, which comprises
(a) forming a first dielectric composition film on a substrate which comprises a nonsilicon containing or substantially non-silicon containing organic polymer; and
(b) forming a second dielectric composition film on the first dielectric film, which second dielectric composition comprises a polymer having a structure selected from the group consisting of I and II:
[Hxe2x80x94SiO1.5]n[Rxe2x80x94SiO1.5]m, 
[H0.4-1.0SiO1.5-1.8]n[R0.4-1.0xe2x80x94SiO1.5-1.8]m, 
[H0-1.0xe2x80x94SiO1.5-2.0]n[Rxe2x80x94SiO1.5]m, 
[Hxe2x80x94SiO1.5]x[Rxe2x80x94SiO1.5]y[SiO2]z,xe2x80x83xe2x80x83I. 
wherein the sum of n and m, or the sum or x, y and z is from about 8 to about 5000, and m and y are selected such that carbon containing substituents are present in an amount of less than about 40 Mole percent; and wherein R, is selected from substituted and unsubstituted straight chain and branched alkyl groups, cycloalkyl groups, substituted and unsubstituted aryl groups, and mixtures thereof,
[HSiO1.5]n[RSiO1.5]m, 
[H0.4-1.0SiO1.5-1.8]n[R0.4-1.0SiO1.5-1.8]m, 
[H0-1.0SiO1.5-2.0]n[RSiO1.5]m,xe2x80x83xe2x80x83II. 
wherein the sum of n and m is from about 8 to about 5000 and m is selected such that the carbon containing substituent is present in an amount of from about 40 Mole percent or greater; and
[HSiO1.5]x[RSiO1.5]y[SiO2]z; 
wherein the sum of x, y and z is from about 8 to about 5000 and y is selected such that the carbon containing substituent is present in an amount of about 40 Mole % or greater; and wherein R, is selected from substituted and unsubstituted straight chain and branched alkyl groups, cycloalkyl groups, substituted and unsubstituted aryl groups, and mixtures thereof.
The invention further provides a process for producing a microelectronic device which comprises:
(a) forming a first dielectric layer on a substrate which comprises a non-silicon containing or substantially non-silicon containing organic polymer;
(b) forming a second dielectric layer on the first dielectric layer, which second dielectric composition comprises a polymer having a structure selected from the group consisting of I and II:
[Hxe2x80x94SiO1.5]n[Rxe2x80x94SiO1.5]m, 
[H0.4-1.0SiO1.5-1.8]n[R0.4-1.0xe2x80x94SiO1.5-1.8]m, 
[H0-1.0xe2x80x94SiO1.5-2.0]n[Rxe2x80x94SiO1.5]m, 
[Hxe2x80x94SiO1.5]x[Rxe2x80x94SiO1.5]y[SiO2]z,xe2x80x83xe2x80x83I. 
wherein the sum of n and m, or the sum or x, y and z is from about 8 to about 5000, and m and y are selected such that carbon containing substituents are present in an amount of less than about 40 Mole percent; and wherein R, is selected from substituted and unsubstituted straight chain and branched alkyl groups, cycloalkyl groups, substituted and unsubstituted aryl groups, and mixtures thereof;
[HSiO1.5]n[RSiO1.5]m, 
[H0.4-1.0SiO1.5-1.8]n[R0.4-1.0SiO1.5-1.8]m, 
[H0-1.0SiO1.5-2.0]n[RSiO1.5]m,xe2x80x83xe2x80x83II. 
wherein the sum of n and m is from about 8 to about 5000 and m is selected such that the carbon containing substituent is present in an amount of from about 40 Mole percent or greater; and
[HSiO1.5]x[RSiO1.5]y[SiO2]z; 
wherein the sum of x, y and z is from about 8 to about 5000 and y is selected such that the carbon containing substituent is present in an amount of about 40 Mole % or greater; and wherein R, is selected from substituted and unsubstituted straight chain and branched alkyl groups, cycloalkyl groups, substituted and unsubstituted aryl groups, and mixtures thereof;
(c) imagewise patterning the dielectric layers to form vias in the dielectric layers extending to the substrate;
(d) depositing a metal into the vias and onto a top surface of the second cured dielectric layer;
(e) removing the metal from the top surface of the second cured dielectric layer.
The invention still further provides a process for producing a microelectronic device which comprises:
(a) applying a first dielectric layer onto a substrate which comprises a non-silicon containing or substantially non-silicon containing organic polymer;
(b) applying a second dielectric layer onto the first dielectric layer, which second dielectric composition comprises a polymer having a structure selected from the group consisting of I and II:
[Hxe2x80x94SiO1.5]n[Rxe2x80x94SiO1.5]m, 
[H0.4-1.0SiO1.5-1.8]n[R0.4-1.0xe2x80x94SiO1.5-1.8]m, 
[H0-1.0xe2x80x94SiO1.5-2.0]n[Rxe2x80x94SiO1.5]m, 
[Hxe2x80x94SiO1.5]x[Rxe2x80x94SiO1.5]y[SiO2]z,xe2x80x83xe2x80x83I. 
wherein the sum of n and m, or the sum or x, y and z is from about 8 to about 5000, and m and y are selected such that carbon containing substituents are present in an amount of less than about 40 Mole percent; and wherein R, is selected from substituted and unsubstituted straight chain and branched alkyl groups, cycloalkyl groups, substituted and unsubstituted aryl groups, and mixtures thereof,
[HSiO1.5]n[RSiO1.5]m, 
[H0.4-1.0SiO1.5-1.8]n[R0.4-1.0SiO1.5-1.8]m, 
[H0-1.0SiO1.5-2.0]n[RSiO1.5]m,xe2x80x83xe2x80x83II. 
wherein the sum of n and m is from about 8 to about 5000 and m is selected such that the carbon containing substituent is present in an amount of from about 40 Mole percent or greater; and
[HSiO1.5]x[RSiO1.5]y[SiO2]z; 
wherein the sum of x, y and z is from about 8 to about 5000 and y is selected such that the carbon containing substituent is present in an amount of about 40 Mole % or greater; and wherein R, is selected from substituted and unsubstituted straight chain and branched alkyl groups, cycloalkyl groups, substituted and unsubstituted aryl groups, and mixtures thereof;
(c) imagewise patterning the second dielectric layer to form trenches in the dielectric layers extending to the first dielectric layer;
(d) imagewise patterning the first dielectric layer to form vias in the first dielectric layer extending to the substrate;
(e) depositing a metal into the vias, trenches and onto a top surface of the second dielectric layer;
(f) removing the metal from the top surface of the second dielectric layer.
The first step in conducting the process of the present invention is to form a dielectric composition on a substrate which comprises one or more polymers selected from the group consisting of poly(arylene ether), a fluorinated poly(arylene ether), fluorocarbons, benzocyclobutene, polyimides and fluorinated polyimides.
The substrate may comprise semiconductor materials such as gallium arsenide, germanium, lithium niobate, silicon and compositions containing silicon such as silicon germanium, crystalline silicon, polysilicon, amorphous silicon, epitaxial silicon, and silicon dioxide, doped silicon dioxide, silicon nitride, and polysilicon, metals such as aluminum, tantalum, copper, and aluminum/copper mixtures, ceramics, polymeric resins, Group III/V compounds and combinations thereof.
Lines may optionally be on the substrate surface. The lines, when present, are typically formed by well known lithographic techniques and may be composed of a metal, an oxide, a nitride or an oxynitride. Suitable materials for the lines include silica, silicon nitride, titanium nitride, tantalum nitride, aluminum, aluminum alloys, copper, copper alloys, tantalum, tungsten and silicon oxynitride. These lines form the conductors or insulators of an integrated circuit. Such are typically closely separated from one another at distances preferably of from about 20 micrometers or less, more preferably from about 1 micrometer or less, and most preferably of from about 0.05 to about 1 micrometer.
The dielectric composition may comprise any of a wide variety of non-silicon containing dielectric forming materials which are well known in the art for use in the formation of microelectronic devices. The dielectric layer may nonexclusively include poly(arylene ether), a fluorinated poly(arylene ether), fluorocarbons, benzocyclobutene, polyimides and fluorinated polyimides. Fluorinated and nonfluorinated poly(arylethers) available under the tradename FLARE(trademark) from AlliedSignal Inc., and copolymer mixtures thereof The dielectric composition may comprise a preformed poly(arylene ether) or fluorinated poly(arylene ether) polymer or pre-polymers in a monomeric state or oligomeric state may be formed on the substrate with subsequent polymerization. Suitable poly(arylene ethers) or fluorinated poly(arylene ethers) are known in the art from U.S. Pat. Nos. 5,155,175; 5,114,780 and 5,115,082. Preferred poly(arylene ethers) and fluorinated poly(arylene ethers) are disclosed in U.S. patent application Ser. No. 08/990,157 filed Dec. 12, 1997 which is incorporated herein by reference. Polyimides and fluorinated polyimides are commercially available from DuPont. Fluorocarbons are commercially available from DuPont under the tradename Teflon or from Asahi Chemicals under the tradename Cytop. Benzocyclobutene is commercially available form Dow Chemicals under the tradename BCB. Other useful polymers include parylene which is commercially available from Novellus under the tradename Alpha. The polymer may be present in the dielectric composition in a pure or neat state (not mixed with any solvents) or it may be present in a solution where it is mixed with solvents. When solvents are present, the polymer is preferably present in an amount of from about 1% to about 50% by weight of the polymer, more preferably from about 3% to about 20%. The solvent component is preferably present in an amount of from about 50% to about 99% by weight of the dielectric composition, more preferably from about 80% to about 97%. Suitable solvents nonexclusively include aprotic solvents such as cyclic ketones including cyclopentanone, cyclohexanone, cyclohexanone and cyclooctanone; cyclic amides such as Nalkylpyrrolidinone wherein the alkyl group has from 1 to about 4 carbon atoms, and Ncyclohexyl-pyrrolidinone, and mixtures thereof Once formed, the dielectric composition is deposited onto a suitable substrate to thereby form a polymer layer on the substrate. Deposition may be conducted via conventional spin-coating, dip coating, roller coating, spraying, chemical vapor deposition methods, or meniscus coating methods which are well-known in the art. Spin coating is most preferred. The thickness of the polymer layer on the substrate may vary depending on the deposition procedure and parameter setup, but typically the thickness may range from about 500 xc3x85 to about 50,000 xc3x85, and preferably from about 2000 xc3x85 to about 12000 xc3x85. The amount of dielectric composition applied to the substrate may vary from about 1 ml to about 10 ml, and preferably from about 2 ml to about 8 ml. In the preferred embodiment, the liquid dielectric composition is spun onto the upper surface the substrate according to known spin techniques. Preferably, the polymer layer is applied by centrally applying the liquid dielectric composition to the substrate and then spinning the substrate on a rotating wheel at speeds ranging from about 500 to about 6000 rpm, preferably from about 1500 to about 4000 rpm, for about 5 to about 60 seconds, preferably from about 10 to about 30 seconds, in order to spread the solution evenly across the substrate surface. The polymer layer preferably has a density of from about 1 g/cm3 to about 3 g/cm3.
In one embodiment of the invention, the first dielectric composition film is applied to the substrate and cured, and then the second dielectric composition film is applied to the cured first dielectric composition film and then cured. In another embodiment of the invention the first dielectric composition film is applied to the substrate and then the second dielectric composition film is applied to the first dielectric composition film and then both films are cured together.
Curing may be done by any means known in the art. Typically the dielectrics are cured by heating to increase its molecular weight. The heating may be conducted by conventional means such as heating on a hot plate in air or in an inert atmosphere, or it may occur in a furnace or oven in air, or in an inert atmosphere, or it may occur in a vacuum furnace or vacuum oven by the application of heat for a sufficient time and at a sufficient temperature to cure the dielectric films. Heating is preferably conducted at a temperature of from about 200xc2x0 C. to about 600xc2x0 C., and more preferably from about 350xc2x0 C. to about 450xc2x0 C. This heating is preferably performed from about 1 minute to about 360 minutes, and more preferably from about 2 to about 60 minutes. Optionally the dielectrics may be cured by electron beam exposure or by exposure to actinic light, such as UV light, to increase its molecular weight. The amount of exposure may range from about 100 mJ/cm2 to about 300 mJ/cm2. The dielectric may be exposed to electron beams in any chamber having a means for providing electron beam radiation to substrates placed therein. Preferably, an electron beam chamber is used which provides an large area electron source. Suitable electron beam chambers are commercially available from Electron Vision, a unit of AlliedSignal Inc., under the trade name xe2x80x9cElectronCure(trademark)xe2x80x9d. The principles of operation and performance characteristics of such device are described in U.S. Pat. No. 5,003,178, the disclosure of which is expressly incorporated herein by reference. The temperature of the electron beam exposure preferably ranges from about 20xc2x0 C. to about 450xc2x0 C., more preferably from about 150 to about 400xc2x0 C. The electron beam energy is preferably from about 1 to about 30 KeV, and more preferably from about 3 to about 10 KeV. The dose of electrons is preferably between about 500 to about 50,000 xcexcC/cm2 and more preferably from about 3,000 to about 20,000 xcexcC/cm2. The gas ambient in the electron beam tool can be any of the following gases: nitrogen, oxygen, hydrogen, argon, or xenon or any combination of these gases. The electron beam current is preferably from about 1 to about 40 mA, and more preferably from about 5 to about 20 mA.
The second dielectric layer comprises a polymer having a structure I or II. Polymers having the structure I are of low organic content where the carbon containing substituents are present in an amount of less than about 40 mole percent. These polymers are described more fully in U.S. patent application Ser. No. 09/044,831, filed Mar. 20, 1998, which is incorporated herein by reference.
In accordance with the present invention, siloxane polymers having the structure with the formulae I:
[Hxe2x80x94SiO1.5]n[Rxe2x80x94SiO1.5]m, 
[H0.4-1.0SiO1.5-1.8]n[R0.4-1.0xe2x80x94SiO1.5-1.8]m, 
[H0-1.0xe2x80x94SiO1.5-2.0]n[Rxe2x80x94SiO1.5]m, 
[Hxe2x80x94SiO1.5]x[Rxe2x80x94SiO1.5]y[SiO2]z, 
wherein the sum of n and m, or the sum or x, y and z is from about 8 to about 5000, and m and y are selected such that carbon containing substituents are present in an amount of less than about 40 mole percent. R, is selected from substituted and unsubstituted straight chain and branched alkyl groups, cycloalkyl groups, substituted and unsubstituted aryl groups, and mixtures thereof. The specific mole percent of carbon containing substituents is a function of the ratio of the amounts of starting materials. In a preferred embodiments the mole percent of carbon containing substituents is in the range of from about 15 mole percent to about 25 mole percent.
In another embodiment of the invention, one may use polymers having the structure II which are of high organic content where the carbon containing substituents are present in an amount of about 40 mole percent or more. These polymers are described more fully in U.S. patent application Ser. No. 09/044,798, filed Mar. 20, 1998, which is incorporated herein by reference. Such have the formulae II
[HSiO1.5]n[RSiO1.5]m, 
[H0.4-1.0SiO1.5-1.8]n[R0.4-1.0SiO1.5-1.8]m, 
[H0-1.0SiO1.5-2.0]n[RSiO1.5]m, 
wherein the sum of n and m is from about 8 to about 5000 and m is selected such that the carbon containing substituent is present in an amount of from about 40 Mole percent or greater; and
[HSiO1.5]x[RSiO1.5]y[SiO2]z; 
wherein the sum of x, y and z is from about 8 to about 5000 and y is selected such that the carbon containing substituent is present in an amount of about 40 Mole % or greater; and wherein R is selected from substituted and unsubstituted straight chain and branched alkyl groups, cycloalkyl groups, substituted and unsubstituted aryl groups, and mixtures thereof The specific mole percent of carbon containing substituents is a function of the ratio of the amounts of starting materials.
Polymers in accordance with structures I and II have a polymer backbone encompassing alternate silicon and oxygen atoms. In contrast with previously known organosiloxane resins, polymers of the present invention have essentially no hydroxyl or alkoxy groups bonded to backbone silicon atoms. Rather, each silicon atom, in addition to the aforementioned backbone oxygen atoms, is bonded only to hydrogen atoms and/or R groups as defined in the formulae. By attaching only hydrogen and/or R groups directly to backbone silicon atoms in the polymer, unwanted chain lengthening and crosslinking is avoided. Consequently, the shelf life of organohydridosiloxane polymer solutions in accordance with the present invention is enhanced as compared to previously known organosiloxane polymers. Furthermore, since silicon-carbon bonds are less reactive than silicon hydrogen bonds, the shelf life of the organohydridosiloxane polymer solutions in accordance with the invention is enhanced as compared to previously known hydridosiloxane resins. In some embodiments, the polymer backbone conformation is a cage configuration. Accordingly, there are only very low levels of reactive terminal moieties in the polymer. This also ensures that no unwanted chain lengthening polymerization will occur in solution, resulting in an extended shelf life. Each silicon atom of the polymer is bonded to at least three oxygen atoms. Moieties bonded to the polymer backbone include hydrogen and organic moieties.
Synthesis of the organohydridosiloxane polymers of this invention may be by a dual phase solvent system using a catalyst. For example, starting materials may be trichlorosilane and an organotrichlorosilane, for either an alkyl or an aryl substituted trichlorosilane. The relative ratios of the trichlorosilane and the organotrichlorosilane determine the mole percent carbon-containing substituents in the polymer.
Polymers of the structures I and II may be prepared by mixing a solution of at least one organotrihalosilane and hydridotrihalosilane to form a mixture; combining the mixture with a dual phase solvent which includes both a non-polar solvent and a polar solvent; adding a catalyst to the dual phase solvent and trihalosilane mixture, thus providing a dual phase reaction mixture; reacting the dual phase reaction mixture to produce an organohydridosiloxane; and recovering the organohydridosiloxane from the non-polar portion of the dual phase solvent system. Additional steps may include washing the recovered organohydridosiloxane to remove any low molecular weight species, and fractionating the organohydridosiloxane product to thereby classify the product according to molecular weight. The catalyst may be a phase transfer catalyst including, but not limited to, tetrabutylammonium chloride and benzyltrimethylammonium chloride. In other embodiments the catalyst is a solid phase catalyst, such as Amberjet 4200 or Amberlite 1-6766 ion exchange resin (Rohm and Haas Company, Philadelphia, Pa.). Such dielectric films formed in accordance with the present invention advantageously provide low dielectric constants, typically less than 2.7. Additionally, dielectric films in accordance with the organohydridosiloxane compositions of this invention exhibit thermal stability permitting cure temperatures of about 425 degrees Centigrade (xc2x0 C.) or greater. In the preferred embodiment, the carbon containing moiety R may be a substituted or unsubstituted straight chain and branched alkyl groups have 1 to about 20 carbons; substituted and unsubstituted cycloalkyl groups may have from about 4 to about 10 carbons and the substituted and unsubstituted aryl groups have from about 6 to about 20 carbons. For example, where R is an alkyl group, R includes but is not limited to methyl, chloromethyl and ethyl groups, straight chain and branched propyl, 2-chloropropyl, butyl, t-butyl, pentyl and hexyl groups. Where R is a cycloalkyl group, R includes but is not limited to cyclopentyl, cyclohexyl, chlorocyclohexyl and cycloheptyl groups; where R is an aryl group, R includes but is not limited to phenyl, benzyl, naphthyl, tolyl and benzyl groups. It will be understood, that the specific carbon content of any specific organohydridosiloxane resin, in accordance with this invention, is a function of the mole ratio of organotrihalosilane(s) to hydridotrihalosilane starting materials employed. Thus, for any R group selected, a resin in accordance with the present invention having a carbon containing substituent present in an amount of less than about 40 Mole % for a type I structure and at least 40 Mole % is provided for a type II structure. Advantageously, embodiments in accordance with the present invention are polymers having a caged structure with a polymer backbone encompassing alternate silicon and oxygen atoms. In particular, each backbone silicon atom is bonded to at least three backbone oxygen atoms to form the aforementioned cage structure. Essentially all additional silicon bonds are only to hydrogen and the organic substituents. Thus, polymers of the present invention have essentially no hydroxyl or alkoxy groups bonded to backbone silicon atoms and crosslinking reactions are suppressed. In preparing the polymers, a mixture of the organic and hydridosilanes (e.g. trichlorosilane and methyltrichlorosilane) is added to a mixture of catalyst, hydrocarbon solvent, alcohol and water. The mixture is filtered, the water is separated, the solution is dried and then evaporated to leave a white solid. This solid is slurried in hydrocarbon solvent to remove monomer and then evaporated to leave desired product that can be formulated in a suitable solvent for use as a spin-on polymer. The molecular weight (Mw) of the product produced can be varied from about 400 and 200,000 atomic mass units (amu) depending on the reaction conditions. It has been found that materials with a Mw of from about 5,000 to about 60,000 amu are desirable. It has also been found that materials with a Mw of from about 10,000 to about 50,000 amu are somewhat more desirable and materials with a Mw of from about 20,000 to about 40,000 amu are most desirable.
The polymer of the upper level dielectric material is dispersed in a suitable compatible solvent and applied onto the lower level dielectric. Suitable solvent compositions include those which have a boiling point of about 120xc2x0 C. or less, preferably about 100xc2x0 C. or less. Suitable high volatility solvent composition nonexclusively include methanol, ethanol, n-propanol, isopropanol, n-butanol, propyl acetate and mixtures thereof Other relatively high volatility solvent compositions which are compatible with the other ingredients can be readily determined by those skilled in the art. The solvent is preferably present in an amount of from about 10% to about 90% by weight of the overall blend, more preferably from about 15% to about 80% and most preferably from about 40% to about 60% by weight of the overall blend with the polymer.
The upper dielectric material may be applied to the coated substrates via the conventional coating methods mentioned above. The thickness of the dielectric film on the substrate may vary depending on the amount of liquid dielectric that is applied to the substrate, but typically the thickness may range from about 500 xc3x85 to about 50,000 xc3x85, and preferably from about 1000 xc3x85 to about 12000 xc3x85. The amount of dielectric liquid applied to the substrate may vary from about 1 ml to about 10 ml, and preferably from about 2 ml to about 8 ml. In the preferred embodiment, the liquid material is spun onto the surface the lower level dielectric according to similar techniques as those mentioned above.
The invention is useful in a single damascene process sequence. Microvias may be formed in the dielectric layers by well known photolithographic techniques using a photoresist composition. The dual layered coated substrate may be imagewise patterned and the removed of portions of the dielectrics form via cavities through both of the dielectric layers. Such are formed in a manner well known in the art such as by coating the top of the upper dielectric layer with a photoresist, imagewise exposing to actinic radiation such as through a suitable mask, developing the photoresist and etching away portions of both of the dielectric layers to form vias. The photoresist composition may be positive working or negative working and are generally commercially available. Suitable positive working photoresists are well known in the art and may comprise an o-quinone diazide radiation sensitizer. The o-quinone diazide sensitizers include the o-quinone-4-or-5-sulfonyl-diazides disclosed in U.S. Pat. Nos. 2,797,213; 3,106,465; 3,148,983; 3,130,047; 3,201,329; 3,785,825; and 3,802,885. When o-quinone diazides are used, preferred binding resins include a water insoluble, aqueous alkaline soluble or swellable binding resin, which is preferably a novolak. Suitable positive photodielectric resins may be obtained commercially, for example, under the trade name of AZ-P4620 from Clariant Corporation of Somerville, N.J. The photoresist is then imagewise exposed to actinic radiation such as light in the visible, ultraviolet or infrared regions of the spectrum through a mask, or scanned by an electron beam, ion or neutron beam or X-ray radiation. Actinic radiation may be in the form of incoherent light or coherent light, for example, light from a laser. The photoresist is then imagewise developed using a suitable solvent, such as an aqueous alkaline solution. Optionally the photoresist is heated to cure the image portions thereof and thereafter developed to remove the nonimage portions and define a via mask. Next the photoresist is completely removed from the dielectric surface and the inside walls of the vias by plasma etching. Plasma generators which are capable of are described in U.S. Pat. Nos. 5,174,856 and 5,200,031.
Next the vias are filled with a conductive metal which fills the vias in area and also forms a layer on top of the hardened upper dielectric. Suitable metals include aluminum, aluminum alloys, copper, copper alloys, tantalum, tungsten, titanium or other metal typically employed in the formation of microelectronic devices. The metal may be applied by such techniques as vapor deposition, sputtering, evaporation, electroplating and the like. The thickness of the metal layer is preferably from about 3000 to 5000 Angstroms. Typically the metal is applied by first forming a barrier metal seeding layer on the walls of the vias and on the top dielectric. Then the balance of the metal is applied. The barrier metal serves to prevent diffusion of the conductive metal into the dielectric layers. Barrier metal may be, for example, a nitride such Ti, TaN or TiN. Next the metal is removed from the upper dielectric layer such as by chemical mechanical polishing or an etch back by techniques which are well known in the art. The hardened upper dielectric layer acts as a polish stop. These steps may be repeated to provide a series of suitable layers and conductive paths over one another on the substrate.
The invention is also useful in a dual damascene process. The first lower non-silicon containing dielectric coating is formed on a substrate and cured. The top of the cured lower dielectric layer is then coated with an upper layer of a high or low organic content, silicon containing dielectric and cured. Trenches are then formed in the second dielectric layer by well known photolithographic techniques using a photoresist composition. The lower dielectric layer acts as an etch stop. The underlying first dielectric layer is then provided with vias by repeating the processing sequence of applying a photoresist layer portion, imagewise exposing through a mask having apertures centered on the trenches but having a narrower diameter. After developing the photoresist and etching away portions of the lower dielectric layer, vias are formed. Next the vias and trenches are filled with a conductive metal which also forms a layer on top of the hardened upper dielectric layer. Next the metal layer is removed such as by chemical mechanical polishing or an etch back by techniques. The hardened upper dielectric layer acts as a polish stop and a microelectronic device results.
The following nonlimiting examples serve to illustrate the invention.